grounding: battery vs. frame

[pianomaniac]

Instructions with the Braille battery charger state to connect the negative to an other (frame or engine) source for grounding. Why not connect to the negative post on the battery? It's a sealed battery. I did anyway!

If you must use another source for ground, where would one find one that's not aluminum,within a short distance of the battery? Thanks.

[LotusLust]

aluminum is a very good electrical conductor. concerned about corrosion?

[FlyLo]

Corrosion, or fire?

The final/ground connection can cause a spark. That's why you're not supposed to connect it to the battery. Batteries can generate hydrogen gas. Boom.

Aluminum is a very good conducter. It's also great for causing electrical fires. That's why it's no longer used for electrical wiring.

I can see why he'd prefer a steel piece, but I have no idea where he'd find one. Is something useful near the tail light wiring? Maybe just fan off the battery really well before you connect to the negative...

[pianomaniac]

Thanks for the posts, guys. Forgive me for my ignorance, please, but.......

Why is it not good for the ground of the charger to permanently share the same post and adjacent connector to the central ground to the battery? It seems to me that if the negative charger lead is connected together with the main ground, they would be one and the same ground connection for all practical purposes. If the main ground doesn't cause a spark, why would the charger lead?

I have a Braille racing batttery. It lays on it's side (sealed) and the positive and negative leads are connected to the battery via phillips head screws. So, on each side I placed the battery round eye connector together with the (permanent) braille charger round eye connector and screwed them together into the battery.

I really do want to understand if this is an unsafe practice but I don't understand how a spark can be caused any easier than one can be caused by it's adjacent connector which is the battery lead. If a problem did exist, I would think that the braille connection is really safely grounded to the cars central ground. Thanks.

[ervsch]

I may be completely wrong, with a problem waiting to happen - and I'd be happy to take anyone's scientific advice...

But, I connected my battery tender directly to the battery posts last winter without any problems - and am doing the same this winter.

[charliex]

the reason is that as said connecting the charger to the negative can cause a spark, so its just a safety issue, a sealed battery still has the ability to vent, are your batteries VRSLB or VRLA, some use replaceable blowoff plugs, the VR types, have a valve that vents at certain pressures (usually due high charging current and at or around 4 psi ) the blowoff types usually need the part replaced.

things could happen

connections work loose

electricity at high voltage/current can arc even when connections are tight, its path of least resistance for the most part, but electricity can be seemingly unpredictable, you can often see sparks in the dark, but sometimes they're tiny.

during charging (generally too fast, but thats not a hard and fast rule) any excess gas thats vented may build up in the trunk, a small spark and its a possible kapow.

pity they mixed up the old red/black positive and negative all those years ago and make people think the black is safer than red ! as well as calling batteries 'sealed'.

normally oxygen is recombined internally, but if the pressure exceeds a certain amount, they will vent, thats the reason.

edit:reworded the charging/gas/trunk part

[ervsch]

Not wanting to be argumentative - but couldn't all of the same things still happen with the charger only connected to the positive terminal?

BTW - I guess I'm a bit better off since I've been leaving the trunk lid open a bit - so no gas build up in the trunk.

[charliex]

if memory serves the hydrogen is vented/created at the positive terminal , so connecting at the negative terminal makes it further away from the gas to reduce the risk of an explosion.though on a VR style battery, the vents may not be at the positive end, but i would imagine they'd stick to the same for consistency with safety protocols.

for other stuff, the habit is the negative, since if you take off the positive first, you risk making a circuit with the spanner and the body, though with the elise this might be harder


also to more complete, gas can also be vented on a discharge as well as a charge, so thinking its just a trickle charger and won't charge too fast is a misnomer.

edit: added of course the spanner thing is for negative grounded frames, some are positive, in which case you'd read the cars manual

[ervsch]

Thanks for the explanation Charlie!

[FlyLo]

The idea is that the spark happens when you complete the circuit, so the last connection you make is best done far from the battery and the potential hydrogen gas. This isn't about continuous sparking. Likewise, you remove the distant (ground) connection first, as this can generate a spark, and you want it far from the battery.

[TimMullen]

Originally Posted by FlyLo

The idea is that the spark happens when you complete the circuit, so the last connection you make is best done far from the battery and the potential hydrogen gas. This isn't about continuous sparking. Likewise, you remove the distant (ground) connection first, as this can generate a spark, and you want it far from the battery.

Yes, and as Charlie pointed out, you should always connect the negative terminal last/disconnect the negative terminal first because of the problem with shorting out the tools used to connect the battery (although it doesn't matter with the Elise).

Most cars are negative ground (at least every car made in the last 40 or so years). That means if the batter is connected, and you are using a wrench on the positive battery terminal and that wrench contacts the metal chassis/engine, you will have a massive spark (I've actually melted away half a screw driver that bumped the positive terminal once). If your wrench connects the negative terminal to ground (chassis/engine), nothing happens since it's already connected to ground. So, if you disconnect the negative terminal first (or connect it last), you can't create a short. Once the negative is disconnected, there is no more circuit to the battery, so if you connect the positive terminal to ground, nothing happens.

Because of the possibility of a spark happening when you make/break the last connection, standard advice is to make that connection to negative/ground away from the battery to allow for the small possibility of a spark causing an explosion (small possibility that there has been explosive gases released that are in the right proportions and still around). Although the possibility of an explosion is remote, it does happen, and some people are severely injured by it every year.

In our Elises, the battery appears to be "sealed", but as Charlie pointed out, even sealed batteries can vent gasses if they are over-charged (they normally don't). But the way, don't confuse "sealed" batteries with "maintenance-free" batteries that are "sealed" so that you don't have to add water - they are not sealed as far as gases being given off.

Bottom line is that most likely the instructions to connect the negative away from the battery is standard legal disclaimer (and good advice). It won't really hurt if you make a permanent connection to the battery posts themselves as long as there are no explosive gases present. My BatteryMinder came with the typical permanent "Ring-eye" connections that extend to a two prong connector (same style as used by the Battery Tender Jr.). I attached the permanent connector to the battery connections, and extended the pig tail to the open area of the boot - not for safety, but for convenience. I plug in my BatteryMinder as necessary, and never give it a second thought. Same set up is also on my Miata (with a sealed battery in it's boot too).

I do wish that the Elise's battery had vent tubes to the exterior similar to what Miata's have - it's a sealed battery, but if it does get over-pressured, the gases are vented to the outside of the boot.

[pianomaniac]

Thanks for the thorough explainations.....you guys are awesome!

[Tyger]

Originally Posted by TimMullen

I do wish that the Elise's battery had vent tubes to the exterior similar to what Miata's have - it's a sealed battery, but if it does get over-pressured, the gases are vented to the outside of the boot.

So that's what that rectangular hole over the license plate is for!